Short-oil alkyd resin of low acid number and methods of preparing the same



Patented Sept. 2, 1952 UNITED STATES PATENT OFFICE.

SHORT-OIL ALKYD RESIN OF LOW ACID NUMBER AND METHODS OF PREPARING THE SAME Robert N. Du Puis, Northbrook, Ill., and Howard J. Wright, Kaukauna, Wis., assignors to Association of American Soap & Glycerine Producers, Inc., a corporation of Delaware NoDrawing. Application May 3; 1946 SerialNo. 667,118.

lClaim. 11 This invention relates toan alkyd-resin'and methods of :preparing the same, .andmore particularly to: an alkyd'resinof low acid number,

low hydroxyl. number, preferably of relativelyble-of-reacting with the-polybasic acid ingredient substantially to. reduce gel formation by cross linkage. As aspecificinhibitor compound may beused aderivative. of an aliphatic hydroxy amino. compound. Other types. ofinhibitors are described I in the 4 following specification- Alkyd resins are prepared from polybasic acids, polyhydric alcohols,.and fatty acids or oils. The

fattyfmaterial serves the necessary purposes of' increasing. solubility and'film flexibility, .but at the same time the film hardness -is decreased'as the fatty content is increased. Moreover, in the usual methods of manufacturing alkyds, when the fatty content is reduced beyond a certain point, say 40 oil length in the case of glycerine resins, the resins have such a high acid number, even after cookingalmost to the gel point, as to therefore of little practical utility. Attempts to prepare short oil-length alkyds by usual methods, therefore, result in soluble resins of high acid be incompatible with most-pigments and are number, or, if it is-attempted to-continue-the; reaction to the point'where a satisfactory "acid number is obtained, in insoluble gels.

Two special methods are known for preparing satisfactory alkyds of short oil length and low acid number which still give hard films. One of these comprises the use of an unusually high excess of glycerine or other polyhydric alcohol, but this. method increases the hydroxyl content of the finished resin to an undesirable degree.

The other special method is to extract certain materials of high oil content from a regular alk-yd by the use of -an aliphatic alcoholas-describedbyWright and Du Puis in Industrialand.

make= a-short-oil resin of low acidnumber' isbelieved to'be-related to the'tendency of a dib'a'sic'acid like phthalic acid and a trior'tetrahydric alcohol like glycerine characteristic of a reaction in which one reactant has at least two reactive groups and the other has more than two reactive groups." When the reaction mixture is' diluted with a" third reactant which has one or at themost two'reactive groups, orif the reactivity of the reactant'with more than two reactive groups is reduced in some otherway,.

the formation of a gel is retarded. Thus, the more fatty acid radicals (greater oil length) in an alkyd, the less tendency to gel (1. e., the resins can be cooked to a lower acid number while still remaining soluble). Moreover, by replacing say glycerine with a monoor dihydric alcohol the gelling tendency is also reduced.

It is theoretically possible to reduce the gelling tendency without reducing hardness, but until now no practical method ofefiecting this result has been known. By the use of our invention, however, it is possible to prepare an alkyd resin ofanyoililength and acid number by the simple procedure of including in the resin formula one of the inhibitor compounds described below; The-result is that within the practical limits set by the. fundamental nature of alkyds themselves, a resin or practically any hardness and acid number can be prepared. This is particularly important in the-case of resins made with :alcohols having more th'an three hydroxyl groups.

The preferred form of newresin is produced by the introduction into the reactionqmass,

either as such or as a chemical derivative, of arelatively small proportion of an inhibitor substance of which the following are typical but not limiting: examples: monoglycerylamine, glyceryl diamine, glyceryl phthalimide, glyceryldiphthalimide, glyceryl succinimide, glyceryl disuccinimide, monoethanolamine, 2-methyl-2-amino-1,

3 propanediol,. gIycerylebeta-naphthyl"' ether,

or; pentaerythritol. to form an insoluble gelwhen allowed to react at elevated temperatures. Such gelvforma-tion is- 3 4 glyceryl monophenyl ether, glyceryl monochlorphthalimides of glyceryl a,'y-diamine and. monophenyl ether, or a hydroxyalkyl amide of a long ethanolamine. The physical constants of these chain fatty acid. materials are as follows:

Per cent N Melting Point, 0.

Phthaliinide of crystallized from Found Theory Found Literature Glycerol a-inonoamine. 151 or methanoL. 6.17 6.33 115-6 New com v pound. Glycerol a,'y-d1a m1ne Methanol 7.89 8.00 209 203-205.

Monoethanolamme H O 7.15 7.33 127-8 126-7.

An extensive series of inhibitor-containin Thedata on a series of twelve alkyds of alkyds and related resinous materials has been to 35% oil length (50.3 to 62% phthalic anhyprepared and tested. Information was obtained dride) made both with no glyceryl phthalimide on the effect of varying: the percent replaceand with varying amounts of glyceryl phthalment f dibaSiC acid y inhibitor; fatty acid imide are given in Table I-A. These data give tent; inhibitor compound used; dibasic a u 20 a comparison between the characteristics of d yp f fa y ac s as the'source of fatty standard short-oil alkyds and alkyds of thesame modifier. Rosin derivatives of hydroxy amines oil length containing glyceryl phthalimide. T

have been prepared and characterized. Since the manner of formulating alkyds seems A preferred inhibitor for s in making the to vary and since terminology may be easily con- W a yd resins of this invention is g y y fused, the actual amounts of reactants which monophthalimide. were used in preparing the resins are given in The most satisfactory method found for the the table. The method of calculation used in preparation of glyceryl phthalimide was the reacformulating the resin batches is given in a later tion between phthalic anhydride and ly y section of this specification. The alkyds were amine: made using soybean fatty acids. All reactants were placed in the flask at the start of the heatco ing period. The mass was brought to 180 C. in 0 NH20Ez0H0H0Hi0H one hour and to 235 C. in the next hour, and 00/ held inthe latter temperature until the desired cure time was reached as determined on a Ther- GO moelectric Company cure plate at 200 C.

\N' CH2 O.HQH CH2OH H20 It is apparent from the data in the table that v the acid number of a resin may be reduced to practically any value depending on the amount One mole of glyceryl amine and one mole of of phthalic anhydride introduced as glyceryl phthalic anhydride are slowly heated in an oil monophthalimide.

Table I-A Alkyd derivatives of glyceryl phthalimz'de Resin N0. 1 2 3 4 5 6 7 8 9 10 11 12 Percent oil length 35 35 35 30 30 30 25 25 25 20 20 20 Reactants (gms):

Phtlialic anhydridc 100. 6 95. 6 90.6 108. 4 95. 4 86.8 116. 2 103. 5 95. 3 124 103. 9 93 Soy fatty acids 67 67 67 57. 4 57. 4 57. 4 47. 8 47. 8 47. 8 38. 3 38. 3 38, 3 Glyceryl monophthalimide 0 7. 4 14. 9 0 16v 4 32. 4 0 18. 8 31. 2 0 30, 1 46, 3 Gly 59. 3 54.8 50. 7 61.1 50. 4 43. 2 63. 3 52. 8 46. 0 65. 5 45. 6 39. 8 Percent Phthalic anhydri 50. 3 50. 3 50. 3 54. 2 54. 2 54. 2 58 1 58. 1 58.1 62 62 62 Percent of the phthalic added as phthalimide 0 5 l0 0 12 20 0 10. 7 13 0 16. 2 25 Acid Number:

d) 93. 0 89. 1 84. 7 96. 3 87. 9 81. 8 87. *1 08. 0 83.0 79. 8 79. 3 '83. 0 H d lNumber as cent g it-1 f 5. 0 4. s 4 6 5. 2 4. 8 4. 5 4. s 5. 4 4. 5 4. 3 4. 3 4, 5 Cure time at 200 0. (sec.) 14 13 p 15 20 15 2O 13 18 28 13 15 X All resins contain 5 percent excess glyceriue based on the weight of the finished product. 1 For method of calculation, see a. later section of this specification.

bath with stirring in an atmosphere of nitrogen. The films described in Table I-B were pre- When the reaction starts the oil bath is removed pared from the resins of Table I-A. They were until the initial reaction, which is very exothercast in duplicate with a Bird film applicator on mic, subsides. Heating is then continued until glass plates except those used in the brittleness the temperature reaches 150 C. The mixture is tests, which were cast on 30 auge tin plate. held at this temperature until water ceases to After baking or air drying the films were stored evolve. at the indicated relative humidity for 2 1 hours The crude products obtained were pale yellow before taking the reported Sward hardness readcrystalline materials which on recrystallization ings. Film hardness at high humidity has been from appropriate solvents became white solids of found to be roughly proportional to water revery well-defined crystalline structure. sistance. The thickness of the films was de- A similar procedure was used in preparing the termined by cutting a 0.5 cm. square out of the aeoarrrs- 5T film in the center of the platezandi meatmring; the thickness all around; this square with an Ames zUprightaGaugeNo. 13twiths- No; IUOLIndiecator.. I

over: an winch mandreh-withima periodi. 015:"2

seconds-e Any:sign ofa pattern. at tlIe -ben'df, as" seen through:a fix 'magnifying "glass; was taken. as: an 1 indication of r brittleness. Since'this is a:

ResinNov. 1 1., I2 is -4.. 5-4 6 7 s- 91 1o. 11 12 Rercentoillengtm "I35. 135* as T302 '30 ,30 25 125- 25- 20 2o 20 PercentThthalieadded'asphthalimide: '10 0 12' '20 0 10.7" '18" 0 161"2 j 25" Films Bakedllhl. at155?f0.:l f. i .1

Sward hardnesslatvappronrel; hum. I

' f5?" 55. .67 .52 60 60;. 52. v76); 73 34 54 52 50 50 56 51 62 69 70 34 38" "40" 30' 33' 33 40- '46 '53-' 57" I 110-. YES YES yes: 'yes.- yes yes yes yes Air Dry Films; 0.65% Pb, 0.05% 00 on I Solids Basis:

Dust-free time, min. 2O 10 18 5 15" 7 14' "10* l5v Tack-free time, min) 30 27 15 20 '20 v 20 15 Sward hardness I at approx. rel. hum. v

1 Average film thickness about 1.1 mil.

taken as an indication of brittleness.

4 Dust-free time'was dtermined by diawinga thread fr0m-a piece of cheeseclothslowlyacross'the e string gnoved jerkil'y; the fihntwas not considered dust-free:

Tack-free time was determined by rubbing a-strip ,of paper into contact withthe film surfaoeand. then pulling ofi the paper; Ifth'ere-was anyaud-iblevidenceof-adhesion when the two surfaceswere" separated,.the film was not considered tack-free;

From Table I-B;it:maybe seen that filmlhard- 30; rather drastic test; some 'of the resins which brittleness are given over a period of 42 days 40 storage-vat fixed relative I humidity;

we have termed brittle would not show" that characteristic:- inother types of" tests.

As" indicated-Lin Table II, the tendency to brittleness is" reduced. without seriousv loss in hardnessxbyreplaoing part. ofl'th'e plithalic anhydride with adipic. acid'or b yblendingbrittle.

with;non-brittle resinsh The latter method is notuof universal. .application;, since 1 some: ofv the medium; oil; alkyd'sr; which area. suitable: plastil- Table II.-Film tests} low temperature bak'es.

35% s0 ao%.so: sm sow 20% so Blend-4 513191111: Blend. 3% E L; Extn; 140%; 0 012 2% GR 0% GP- 5% GP A B o k Res.l 1L0.

Acid No 9.2 14.3.- sue 10.1; 940- 5.8? 1 6. 41 3 6, 1 Sward Hardnessz 1 1 ts; h 9' 15 32 13- 12 12 6 14- m r 10 v 1s 21 19- 25-v 8'- a2 2 20' 25 47 22 2T 2 3 50%rel;hum 21 151 22 35 1e 242 30 26 31 22v .relhhum 7 1 13V 15 1s 12 19." 20 13: 26 10" Longer storage at indicated" lei'..'hllm'.' .7 daysr;

O%-re1."hum 50% rel; hum 30 days:. 7 i

0% rel. hum 50% rel. hum 42 days: v 50% rel. hum: i Brittleness: 5

Cold 4 no no no noyes' yes no: yes yes no yes YES no no no no no no" yes mm 1105 yes 1101, no: 1 no" yes yes no yes.- yes, I not no. yes yes" yes yes yes no' 1 All experimental alkyds contain 5 excess glycerine basis finished resin: Allfil'ms bakedfltl'minutesat 83G. using 0.01% I Cobasissolids: 4% Glyceryl-phthahmlde means'4%-ot-thephthahcanhydr-ide was replaced with an equivalent amount of glyceryl phthalirnide. SO =soybean. oil

GP glyceryl phthalimide LO=li'nseed oil Average filmithickness about 1.1 mil.

3 Hardness taken immediately after removal from the oven.. 4 Hardness taken when films had cooled to roomtemperaturea 5 Brittleness tests were made by bending a tin plate on which the,

filnrhadibeen dried over a 14-inch mandrel within 2 seconds.

Any pattern at the bend as seen through a 6X magnifyingglzissavastaken asan indication of brittleness.

The brittleness test used in evaluating. the: films comprised bending thetin plate and film cizersl: as.a.dipic acid in reducing brittleness.

shorter oil; imideeresins are :incompatible with Sebacic acid has about the same efi'ect amount of fatty acids maintained at about 220 C. in an atmosphere of nitrogen. An atmosphere of carbon dioxide leads to unsatisfactory results under these conditions. The amides are practically neutral waxy materials with hydroxyl contents corresponding to the expected structure RCONHCH2-CHOHCH2OH.

Alkyds prepared from fatty acid amides of glyceryl amine, phthalic anhydride and glycerine had greatly improved film characteristics inv comparison with those of ordinary alkyds, and like the other inhibitor-containing alkyds showed the additional important advantage of Sward Hardness Baked Percent OH NO for 1 hr. at 150 0. Oil Glyceryl P. A. Acid Uncut: Length Imide Used Subst. No. meted bylmide 0% 50% 100% R. H. R. H. R. H.

Percent 30 Succinimide 13. 2 70. 2 56 54 39 30 Pthalimide. 13. 2 11. l 76. 2 54 47 38 Although most of the resins in this study were made with the use of fatty acids rather than triglycerides because of convenience, it was found that both sources of fatty acid modifier can give satisfactory alkyds. For example, the oil can be alcoholized with glyceryl amine or other hydroxy material, after which the other ingredients can be added in the usual manner, but these resins tend to be dark. Also, after alcoholysis with glycerine, the phthalic anhydride, glyceryl amine and glycerine could be added, but this too gives dark resins and requires cooling at the time of mixing because of the violence of the reaction between phthalic anhydride and glyceryl amine at elevated temperatures. The preferred procedure is to alcoholize with glycerineaccording to standard practice, and then add glyceryl phthalimide, phthalic anhydride and glycerine.

Inhibitor-containing alkyds modified with linseed fatty acids were prepared from linseed oil as well as from linseed acids. These resins were not greatly different than those modified with soybean fatty acids.

The characteristics of the new alkyds are such that they are adapted to uses where ordinary alkyds are entirely unsuited. For example, new resins of very low acid and hydroxyl numbers and down to zero oil content can be made and are of potential usefulness in the plastics industry, since they are initially rather high-melting and give off only negligible amounts ofwater on further heating or polymerization. These alkyds are indicated for use in heat-sealing compositions because of their satisfactory melting point range, toughness, good adherence and flexibility in proper oil length.

As another example of the process, the amides of glyceryl monoamine (l-amino propanediole 2,3) were employed. These amides were prepared by dropping the amine into the equivalent I retarded gelation during resin cooking, to the extent that resins of very low oil content and very low acid number could be produced.

It is believed that when a N-substituted amide is introduced into the reaction mass, a new reaction which we have termed amide interchange takes place and the basic nitrogen is ultimately transformed into an imide of the dibasic acid used- This reaction takes place according to the following equation in the presence of alco holic hydroxyl groups 21.4 parts glycerylphthalimide, or V 21.2 parts glyceryl alpha- (beta-naphthyl) ether,

or 7 .3 parts propylene glycol, or

16.0 parts glyceryl alpha-phenyl ether, or

19.4 parts glyceryl alpha-p-chlorophenyl ether, or

19.4 parts glyceryl alpha-o-chlorophenyl ether.

Sward Hardness, 1 hr. Uncorbaked at 0. Acid reciiid 0 Number 50% RH I0 glycerine-may be reduced to 'two so that theresin is substantiallywa linear polymer.

.1. Fatty .acids' in combination with 'g'lycerine reduce its functionalityto two or even to one by the formation of monoor 'diglycerides.

2. .In a v similar way, phthalic .arihyd'ride which reacts only partially with glycerine reducesIthe functionality of glycerine. Since this type .of action leaves unreacted. carboxyl groups which 'show up as the acid number of the resin, it may be said for the sake of simplicity that control .of acid number affects the .functionality of 3. iExcessshydroxyl groups in. an alkyd. constitute the third method of reducing'therfunctionality of glycerine. If thereis for'exampl'e, one

Sward Hardness, 1 hr. baked at Uncor- 150 .C. rected Aeid N EJ 0 7 50 7 1007 Q i um er a 0 0 RH RH RH B i oil. All glycerine subst. by P. E. 5% 1 I f i excess OHs 87.4 51.9 59 V 62 "46- uNo 40% oil. All glycerine subst. by P. E. 23.3% 1 P. A. subst. by glyc. phthalimide 5% excess t OH 77. 7 19. 7 56 40 25 N0 oil All glyc. subst. by P. E. 5% excess OH 53.8 33. 6 56 348 25 ":No 50% oil, All glyc. subst. by P. E. 13.5% P. A. a

subst. by glyc. phthalimide 5% excess OHs. 71.8 9.1 45' "'37 27' 'No' I Glyceryl phthalimide has averymarked effect on the acid number of pentaerythritol resins. Heretofore the resins gelled-before a lowacid number could be attained due-tosthe four :primary hydroxyls in the alcohol. The "addition of the imide makes possible the reduction of the acid to the desired value without danger of gelation.

The second example in :the preceding table was formulated-so as to give .an acidnumber of.l3.7'accordingto the method of calculation described later in this specification. The observed value of 19.7, which is in reasonably good agreement with the theoretical value considering the type of resin, could of course have been reduced further by using a larger percentage of glyceryl phthalimide.

As heretofore explained, it is believed that-the use of the inhibitors has an effect in reducing cross linkage. This theory is borne out by the evidence already presented and further has been checked by application'of a method of calculation based on a theory which predicts the acid number of the finished product.

Given the fatty acid and excess hydroxyl content,- the calculationdirects the preparation of a resin by showing-the amount of inhibitor compound which must be used-to reduce the acid number to the desired value.

Inexplaining the results found, and as a basis for predicting the results in other compositions, equations were derived based upon certain assumptions as follows: It is assumed that alkyd polymerization in the kettle is predominantly linear, and that the functionality of all polymerizingv constituents may be considered as two in the finished resin. Any constituent such as v glycerine which has a potential functionality of more than-two is assumed not to use more than two. functional groups to any great extent.

Taking the standard glycerinephthalic .anhydride-fatty acid alkyd as an example, it is seen that glycerine is the only ingredient having a functionality greater than .two. There are three methods by which the functionality of the 5 Percent oil (oil length) IOU-percent mole of free glycerine in a resin, there'arethree equivalents of free hydroxyl groups. .This excess glycerine is not present as-such, .but is probably made up of one free hydroxyl group from .each of three glycerine residues. Therefore,.onemole equivalent of free glycerine in a resin will render three moles of :glycerine diareactive. 'This method of reducing the functionality of glycerine, which means controlling .the "gelation of alkyds in the kettle, is one of the most important, and can :be easily expressedintermsof thehydroxyl number ofthe-resin 'It isassumed that the onlymeaction occurring in the ,-resin kettle, except possible amide .inter- .change,is .esterification. .This .is :believed .to .be substantiallytrue.

, In the case of a. tetrafunctional. material :like

pentaerythritol, it is assumed that when free hydroxyl groups are present, there are two of them on each pentaerythritol .residue. Thus one mol equivalent of pentaerythritol is capable of rendering only two moles of pentaerythritol direactive.

All .resins'rwere .cooked'toaacure=time-iof about 20 seconds :on a Thermoelectric Company rhot ;.plate at 200 Cgwhich is believed "to *be'as .close to "the gel point of the resin :as is practical. Since methods :of calculating the :formulas of regular alkyds are not standardized, athe-calculation procedure-will be carriedthrough'fromthe beginning. Repeated checks of the "method on laboratory batches of :resin have resulted in .remarkably. close agreement of theory and ;practies. The procedure assumes no loss of phthalic anhydride or other ingredient from the-kettle during cooking.

In the following paragraphs, the identity '01 numbers otherwise unidentified is as-follows:

92=moL wtUglycerine l36=mol. wt. pentaerythritol 280=av. mol. wt. soybean oil fatty acids '56,108=mg. per mol. KOH

221=mol. wt. glyceryl phthalimide alcohol phthalate.

i1 Percent alcohol phthalate=percent 'phtli'alic anhy- W. phthalate M. W. phthalic anhydride For glycerine, the latter facte'r=1.29. To. make 2: grams of resin containing y percent excess alcohol based on the weight of the finished product, calculated as follows? dride desired times Grams phthalic anhydride:

percent phthalic anhydride-z v 100 Gramsfatty acid=percent oil-x-percent fatty acid in ester. (Percent fatty acid in ester=95.7 for glycerine. If oil is used to make the resin, simply i percent oil-:2) V 100 Grams alcohol= mg. KOH equivalent to acid groups hydroxyl number of acohol +(m'y) To predict the acid number of a resin from its formula, the assumptions regarding the substantially linear structure of alkyds and the methods by which glycerine is rendered difunctional are carried out as follows. Specific examples will be given in order to clarify the explanation.

An alkyd of 40% oil length containing the equivalent of 5% excess glycerine based on the entire resin can be made from the following ingredients:

76.5 g. soy fatty acids 93.0 g. phthalic anhydride 58.2 g. glycerine Weight of finished resin, 210 g.

The fatty acids would render The g. excess glycerine would render 10-3=30 g. glycerine direactive.

This leaves 58.2-(25+30)=3.2 g. tri-reactive glycerine which must be made di-reactive by forming a half-ester of phthalic anhydride, leaving an equivalent amount of free acid groups, which will be responsible for the acid number of the resin. In this case, the predicted acid numher is =25 g. glycerine direactive 94.6 g. soy fatty acids 75.0 g. phthalic anhydride 57.0 g. pentaerythritol Weight of finished resin, 211 g.

The fatty acids would render 94.6X136 2X28O The 10.55 g. excess P. E. would render 10.55 2=21.1 g. pentaerythritol direactive =22.9 g. pentaerythritol direactive 12 This leaves 57-(22.9+21.1 =13 g. tetrareactiv pentaerythritol, which must be made direactive by forming a half-ester of plithalic anhydride. The predicted acid number of this resin is 13 X 2X56108 136X211 In an experimental batch using the above formula, the acid number obtained was 33.6.

If it is desired to reduce the acid number of the above formula to 10 by replacing part of the phthalic anhydride with glyceryl phthalimide. the formula is revised in accordance with the following calculation. An acid number of 10 would allow the presence of 136X1OX211 2 56108 Therefore in the above formula 13-2.5=10.5 pentaerythritol must be replaced with which in turn would replace =25 g. tetrareactive pentaerythritol =17.1 g. glyceryl phthalimide 11.45 g. phthalic anhydride The formula for the new batch of predicted acid number 10 wou d then be 94.6 g. soy fatty acids 63.55 g. phthalic anhydride 46.5 g. pentaerythritol 17 .1 g. glyceryl phthalimide.

In an experimental batch using the above formula, the acid number obtained was 9.1.

In the following example, it will be shown how to calculate the amount of glyceryl phthalimide necessary to reduce the acid number of a 30% oil glyceryl phthalate alkyd to the desired value.

A 30% oil alkyd containing 5% excess glycerine on the basis of the finished resin can be made from the following ingredients:

57.4 g. soybean fatty acids 108.4 g. phthalic anhydride 61.1 g. glycerine Weight of finished resin, 210 g.

The fatty acids would render 2 2-09 13 9 glycerine direactive The 10 g. excess glycerine would render 10-3=30 g. glycerine direactive.

This leaves 61.1(l8.9+30)=12.2 g. tri-reactive glycerine, which must be made direactive by forming a half-ester of phthalic anhydride. The predicted acid number of this resin is Tia-iii? In an experimental batch using the above formula, the acid number obtained was 32.7.

If it is desired to reduce the acid number of the above formula to 10 by replacing part of the phthalic anhydride with glyceryl phthalimide, the formula is revised in accordance with the following calculation. An acid number of 10 would allow the presence of 3.4 g. trireactive glycerine 13 Therefore in the above formula 12.23.4=8.8 g. glycerine must be replaced with =2l.2 g. glyceryl phthalimide A which in turn would replace 57.4 g. soybean fatty acids 94.2 g. phthalic anhydride 49.4 g. glycerine 21.2 g. glyceryl phthalimide In an experimental batch using the above formula, the acid number obtained was 11.6.

Additional examples of the correlation between predicted and observed acid numbers using the method of calculation described are given in Table I-A as Acid Numbers Calculated. Finished batches of resin in all cases weighed 210 g. The calculations were made according to the following formulas:

(a) For resins not modified with glycery] phthalimide:

Acid number fatty acids-mol wt. gly. M01. wt. fatty acids um dioxide was still tacky at the end of one hour and had a hardness of only 10 after 72 hours. The same imide substituted resin air dried under 0% relative humidity, had a hardness of 20 at the end of one hour, while the Glyptal resin was still tacky. At the end of 72 hours under these conditions the Glyptal resin still had a hardness of only 16.

As is well known in the art, it is diiiicult and sometimes impossible to duplicate film hardness readings with a given resin preparation on successive days even under rigidly controlled conditions. Atmospheric conditions including temperature and relative humidity have some bearing on results of hardness tests. Therefore we do not wish to be bound by the numerical film hardness data given under the heading Sward Hardness, in this specification, or the relationships between resins implied therein, but only by the wording of the following claim.

We claim:

A short'oil alkyd resin having an acid number below 15 and being capable of acting as the sole film-forming constituent in a surface coating composition, comprising essentially the reaction product of 20 to 40 mole per cent of glycerine, 40 to mole per cent of phthalic anhydride, 10 to 20 mole per cent of a vegetable oil fatty acid, and between 5 and 15 mole per cent of glyceryl monophthalimide, wherein the fatty acid plus the glyceryl monophthalimide comprises approxi- +3-wt. excess gly.)]mg. KOH per mol mol. wt. g1y.-wt. finished resin (b) For resins modified with glyceryl phthalimide:

Acid number=Ca1cd. acid No. of unmodified resin- =2.91 [Wt. g1ycerine((0.329-wt. fatty acids)l30)] M01. wt. glyceryl phthalimide-wt. finished resin =Ca1cd. acid No. of unmodified resin- (1.21-wt glyceryl phthalimide used) The method of calculation and the theory outlined above can readily be adapted to types of alkyds other than those specifically mentioned as well as to mixtures.

Aliphatic dibasic acids such as adipic and sebacic may also be used, particularly in substitution for part of the phthalic anhydride. Similarly maleic and fumaric acids may be employed.

The inhibitor-containing alkyd resins are most remarkable because of their unique combination of properties. For the first time an alkyd is made available with an acid number below 15, and even below 10, which forms films which are non-brittle and yet have a hardness comparable to that of the best alkyd resins heretofore obtainable. These new resin films can be dried so rapidly through the tacky stage as to permit air drying of the resin in one hour or less. Such films are made available for air drying assembly lines. For example, a 30% oil length alkyd resin having 13.2% of phthalic anhydride substituted with glyceryl phthalimide in xylene solution and ground with titanium dioxide to produce a white enamel. dried to a Sward hardness of 12 in one hour under relative humidity. A standard Glyptal 2452 resin similarly treated with titanimately 20 to 25 mole per cent of the reaction mixture.

ROBERT N. DU PUIS. HOWARD J. WRIGHT.

REFERENCES CITED The following references are of record in the file, of this patent:

UNITED STATES PATENTS Great Britain Aug. 18, 1932 

